The short talk (<= 20 minutes) is a fixture at most scientific
conferences. Assuming that you have an overhead projector, this note focuses on
how to give a good short talk.

I think that if you can give good short talk then you can probably give a
good 50-minute presentation because the additional time permits a certain
flexibility. For example, in a 50-minute talk I think that the speaker can risk
losing the majority of listeners for 10 minutes while a technical aspect is
embellished for the "experts". In contrast, the short talk requires a more
sustained level of clarity if it is to be successful.

Perspectives

It is more profitable to dwell on the positive aspects of the short talk
framework than to stew over why you were not given a longer time to speak. Here
are some perspectives:

A short talk is a long abstract. If a one-hour talk corresponds to
a paper, then a short talk corresponds to a long abstract. It should
communicate without distracting detail.

A short talk is a captivating lead paragraph. For a reporter, the
quality of that lead paragraph will determine who reads on. A successful short
talk will encourage the listener to ask questions, or to buttonhole you
outside the lecture hall, or to pursue your literature pointers.

A short talk is a commercial. It is a great occasion to advertise
your research accomplishments and/or expository skills. But unlike a prime
time spot on network TV, it should give an accurate picture of the
product!

The right perspective depends on the audience. Are you speaking to
undergraduates, a small group of research friends, visitors from a granting
agency, or drop-ins at a large multi-session conference?

Content and Structure

Amount of Material. Resist the temptation of cramming too much into
your talk. This is perhaps the greatest pitfall of the short talker and the
underlying psychology is clear:

"What I have to say is too important to be edited down to my allotted
time."

"If I do not overstock my talk, then the audience will think that I do not
have much to say."

The crammed short talk is a negative statement. It indicates that the speaker
is incapable of editing for importance. Of course, crammed talks are often the
consequence of personal enthusiasm for the material. But recognize that it is
possible to edit what you say without editing your enthusiasm.

Audience Make-Up. If you have a heterogeneous audience, then you may
have to make hard decisions with respect to the assumed level of expertise. No
one will be happy if you appease the unprepared with ten minutes of background
notation and then placate the expert with ten minutes of rigorous minutia. The
best course of action is to peg your talk at a level of expertise that suits
your goals. State those goals early on and apologize (once) to the potentially
offended parties.

Organization. Like any presentation, a short talk should have a
beginning, a middle, and an end. Start with an outline of the problem and why it
is important. Then delineate the central contribution with suitable pointers to
related work. Do not end with references but with a conclusion. Repeated slides
are a good way to emphasize important points. For example, at the end of your
talk you may want to display an early slide that itemizes the main points of
your talk.

References and Acknowledgements. Be gracious, especially if people
in the audience are involved. Vague collaborators can be listed on your opening
slide.Specific collaborations and references (by name) should appear "in-line".
Stepping through a brief bibliography is one way of outlining related work.
There is not much point in giving complete bibliographic information on a slide,
but be prepared to provide reference details should there be a question.

Algorithms and Proofs. The presentation of algorithms and proofs
requires great care. If a low dimension example captures the essence of an idea,
then use it. If you feel that a step-by-step approach is instructive, then be be
informal enough so that the whole thing fits on a single slide. If the enforced
brevity is too disruptive, expand selected details on subsequent slides.

Benchmarks and Data. With respect to benchmarks and other
statistical data, remember that facts do not speak for themselves. A few well
chosen results can enliven a talk and clarify difficult concepts. Too many
statistical results again point to a speaker who is incapable of editing.

Anticipating Questions. After you have finished writing your talk,
think of the three most likely questions that might be asked. If any of these
are particularly "nasty", then you should revise your talk with an eye towards
heading off potential embarrassment. The impression that people have of your
work will be more positive if its shortcomings are delineated by you and not by
a member of the audience.

The Delivery

How well your short talk is received is as much a function of delivery as
content. Here are a few pointers.

You do not have to say everything that is on a slide. For example, the
audience can read an equation faster than you can speak it.

Concentrate on the audience and not the projection screen. If you must
reference an item on your slide, point to the screen with a pointer or point
to the slide with a pencil. The latter is preferable with large audiences.

Do not fixate on a V.I.P. who happens to be in attendance. It will
bother the rest of the audience and you will appear too eager for
approval.

Have a pen available and be prepared to mark a slide in response to a
question.

Avoid the peek-a-boo style of gradually uncovering a slide to force the
audience to read along with you. The transparency is a different medium than
the blackboard and it is better to gracefully accept its disadvantages. If you
want to reveal the items on a slide one at a time, then use overlays or
separate slides for each item.

Give the audience 4-5 seconds to scan a slide before you begin talking
about it.

If you have a dramatic one-liner, then have a slide with just that
one-liner.

Do not hardwire jokes into your talk by placing them on a slide. It is
better to let the humor level be established dynamically as your talk
unfolds.

Never apologize by saying "there is not much I can do in such a short
talk." If you feel that way, then you have no business giving a short
talk.

Write clear slides. Marker pens are not necessarily inferior to
advanced slide-producing systems. However greater clarity can result if you
typeset as it forces you to think a little more about content and visual
appearance. If you use pens, use just a few colors and use them consistently.
Avoid cutesy icons. In any case it is difficult to imagine a nice slide that
has more than 7-8 lines of material. If there is a lot you want to say with
respect to certain slides, then shuffle handwritten notes into your stack of
transparencies.

It is fine to piece together slides from different talks. But make sure the
styles mesh so as not to telegraph the fact that you are cobbling together
material from prior presentations.

Never use a slide that is a photocopy of a journal article or report. The
printing will be too small and it will be a tell-tale sign that you have not
sufficiently edited your talk.

Practice your talk to anticipate time of delivery. It is helpful to
identify "dispensable slides" which can be jettisoned without damage should
you run out time. Keep a subtle eye on the clock or have a friend in the
audience give you an agreed upon signal when it is time to wrap things up.

Of course, you should end with the usual "are there any questions?"
Unfortunately, if no one raises their hand then (right or wrong) negative
conclusions are reached. The best guard against this is to set an appropriate
pace. If you arrive breathless at the end of the talk, then the mood is not
conducive to questions. Another trick is to relate your talk to the work of
somebody in the audience. That person will often feel obliged to
comment.

Conclusion

In the end it takes practice. Expect to blow away a few audiences
before you deliver your first twenty-minute masterpiece!